A default configuration file,default.properties, that is loaded on startup.
This file is not editable, but you can read it to determine default settings
and find the exact names of properties you want to change.

An installation configuration file,install.properties, containing any properties
specified when Message Queue was installed. This file cannot be edited after
installation.

In addition, each individual broker instance has its own instance
configuration file, as described below. If you connect broker instances
in a cluster, you may also need to use a cluster configuration file to
specify configuration information for the cluster; see Cluster Configuration Properties for more information.

At startup, the broker merges property values from the various configuration
files. As shown in Figure 4–4, the
files form a hierarchy in which values specified in the instance configuration
file override those in the installation configuration file, which in turn
override those in the default configuration file. At the top of the hierarchy, you can manually override any property
values specified in the configuration files by using command line options
to the imqbrokerd command.

Figure 4–4 Broker Configuration Files

Editing the Instance Configuration File

The first time you run a broker, an instance configuration file is created containing configuration properties for that particular broker instance. The instance configuration file is named config.properties and is stored in a directory
identified by the name of the broker instance to which it belongs:

The instances/instanceName directory
and the instance configuration file are owned by the user who created the
corresponding broker instance. The broker instance must always be restarted
by that same user.

The instance configuration file is maintained by the broker instance
and is modified when you make configuration changes using Message Queue administration
utilities. You can also edit an instance configuration file by hand to customize
the broker’s behavior and resource use. To do so, you must be the owner
of the instances/instanceName directory
or log in as root to change the directory’s access
privileges.

The broker reads its instance configuration file only at startup. To
make permanent changes to the broker’s configuration, you must shut
down the broker, edit the file, and then restart the broker. Property definitions
in the file (or any configuration file) use the following syntax:

propertyName=value [[,value1] …]

For example, the following entry specifies that the broker will hold
up to 50,000 messages in memory and persistent storage before rejecting additional
messages:

imq.system.max_count=50000

The following entry specifies that a new log file will be created every
day (86,400 seconds):

Setting Configuration Options from the Command Line

You can enter broker configuration options from the command line when
you start a broker, or afterward.

At startup time, you use the Broker utility (imqbrokerd)
to start a broker instance. Using the command’s -D option,
you can specify any broker configuration property and its value; see Starting Brokers and Broker Utility for more information. If you start
the broker as a Windows service, using the Service Administrator utility (imqsvcadmin), you use the -args option to specify
startup configuration properties; see Service Administrator Utility.

You can also change certain broker properties while a broker instance
is running. To modify the configuration of a running broker, you use the Command
utility’s imqcmdupdatebkr command;
see Updating Broker Properties and Broker Management.